igoi] DowLiNG — Red Riyer Valley. 119 



One line along- which it is evident the edge of this glacier 

 made a halt as shown by an extra amount of boulder-clay, is along 

 the western margin of the Duck mountains then southward skirt- 

 ing the eastern bank of the Assiniboine river, ciossing to the 

 south side through the Brandon hills and by the Tiger hills to the 

 Pembina mountain. There is evidence that a lake filled the valley 

 of the Souris and part of the Assiniboine, while the ice front was 

 at this line. (This is ouclined in the second illustration.) The 

 drainage of this lake was to the south-east along the foot of 

 the glacier and the scouring of this large stream wore a great 

 valley through which now runs a small stream — the Pembina river. 

 The change in drainage was accomplished by the further melting 

 of the ice so that the Assiniboine and the Souris rivers united in 

 the present valley. 



The retreat of the ice down the Red River valley was accom- 

 panied by the formation of a large lake at its southern margin, for 

 the water was obliged to accumulate till it found an outlet, which 

 in this case was to the south through what is now Lake Traverse to 

 the Mississippi. As the retreating front passed farther north the 

 lake grew in dimensions and beaches were formed along its shores. 

 There is evidence that another great invasion of ice this time from 

 the north-east, was threatened but its margin did not probably 

 cover the entire basin. It still held the water, as a long inland 

 sea, from draining to Hudson Bay. During this period the 

 removal of the weight of the former glacier from the earth caused 

 a gradual rising of the land at the north to probably its previous 

 elevation and maintained the flow of the waters of the lake to the 

 southward. This rise was continued as the second glacier dis- 

 appeared and there came a time when the water found other 

 outlets probably toward Hudson Bay and a gradual contraction of 

 the lake ensued in which successive beaches mark the different 

 stages. 



The evidence of the former occupation of this great plain by a 

 vast lake is clearly shown in the beautiful beaches in Manitoba, 

 Dakota and Minnesota. These have been examined, traced and had 

 their levels determined. In the tracing and levelling it was dis- 

 covered that instead of being laid in level rows, the surface of 

 the higher ones rise to the north at a rate increasing from six inches 

 to one foot in the mile. The lower ones are more nearly level as 

 is the case of the lowest or those at present around the present 

 lakes. This is the evidence of the upward rise of the land to the 



